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 756 POSTAGE STAMPS POTASH from and 13,693,056 received in the United States. The total cost of the United States ocean mail steamship service (including $662,- 500 paid from special appropriation for steam- ship service to Japan and China, to Brazil, and to the Hawaiian islands) was $994,844, of which $235,373 was paid for the transat- lantic service. See Geschichte der preussischen Post, by Henry Stephan (Berlin, 1859) ; " Her Majesty's Mails," by William Lewins (London, 1864) ; " A History of Banks for Savings," by William Lewins (London, 1866) ; Notice sur Vorigine du prix uniforme de la, taxe des let- tres (Paris, 1872); and Histoire de la poste aux lettres depuis ses origines les plus an- ciennes jusqu'd nos jours, by Arthur de Roth- schild (Paris, 1873). POSTAGE STAMPS. The system of prepaying postage by means of small adhesive labels, to be sold to the public and received by the post office in evidence of payment when attached to letters, was first advocated by Rowland Hill in 1837, and was adopted by the British post office in 1840, the stamps being first used on May 6 of that year. They were introduced into the United States in 1847. The designs on postage stamps vary greatly with the time of issuing and the different nations that employ them. The first adhesive stamp issued by Great Britain consisted of a profile of the queen, with the word " Postage" above and the value below ; but this design was objected to by many governments on account of the seeming disloyalty of the blackening (in cancellation) of the portrait of their sovereign. Brazil, the second country which adopted the system, used a simple figure of value, rather large, which was eventually superseded by a portrait of the emperor. The various German states seem to have a preference for numerals of value sur- rounded by inscriptions, which were at first printed in black on colored paper; but this style of printing soon gave way to the more secure plan of printing with colored ink on white paper. Many countries have adopted the national arms as the principal design of their postage stamps, and most of the stamps printed in Europe are impressed on paper watermarked with some appropriate design as an additional protection against counterfeiting. The invention of the perforating machine in England, which enabled the stamps to be more readily separated from each other, was soon adopted universally. More varieties of postage stamps have been issued, and a greater number have been in use at one time, in the United States than in any other country. Thus the total number of varieties issued is 162, while 127 have been in use at one time. Only 32 varieties have been issued by Great Britain, and 60 by France. Postage-stamp collecting, or "philately" (Gr. 0/Aof, loving, and arMeia, tax-free), as it is now called, began as soon as stamps were in use in half a dozen countries, and many volumes have been published on the subject. There are also special periodicals de- voted to it, among which are the " American Journal of Philately," now (1875) in its llth volume ; Le timbre poste (Brussels) ; the Brief - marken-Anzeiger (Berlin) ; and " The Philate- list" (Brighton, Eng.). For a description of all postage stamps issued, see J. W. Scott's- "Postage Stamp Catalogue" (New York). POTASH, or Potassa, the name usually given to the hydrated oxide of potassium (potas- sium hydroxide), or caustic potash. Aristotle is one of the earliest writers who mention it. He says that the Imbrians were in the habit of preparing a lye from the ashes of reeds and plants ; and Pliny calls the salt made from the ashes of the oak nitrum. The difference- between soda and potash was not recognized by the ancients. The alchemists were of the opinion that the alkali of plants was the pro- duct of combustion, the same as the gases, and it was not till 1764 that its presence in the unburned plant was shown by Marggraf. The difference between soda and potash was recog- nized in 1735 by Duhamel, and the presence of potash in minerals was detected in leucite by Klaproth toward the end of the last century. As soil is formed by the disintegration of rocks, the fact that plants take up the potash from the ground as nourishment soon became known, and the alkali in animals was traced to the food also indirectly derived from the soil. The importance of potash to the growth of plants and animals thus became apparent, and the study of this compound has long oc- cupied the attention of chemists. Potassium hydroxide, or caustic potash (HKO), is of great importance in the arts, chemistry, and phar- macy, not only as the base of numerous use- ful salts, but for its own independent prop- erties. It is commonly prepared from the car- bonate, a solution of which in 10 to 12 parts of water is boiled with about an equal quanti- ty of freshly slaked lime, made in a paste with water, and gradually added to the solution. The boiling is performed in a clean iron ves- sel, and is continued for about half an hour. The lime seizes the carbonic acid of the car- bonate of potash, and leaves the hydrate of potash in solution ; and the operation is found to be complete when no effervescence is ob- served on taking out a portion of the liquid and adding a little hydrochloric acid. It may then be drawn off in part from the calcareous, sediment, and the remaining portion be recov- ered by filtering through a cotton filter, pro- tected as much as possible from the air, by which it might again be partially carbonized. The clear solution is now evaporated rapidly in a polished iron or silver vessel, till it be- comes of an oily consistence and hardens on cooling. Before it is allowed to cool it is usu- ally run into cylindrical moulds, and thus is formed in sticks, which are the caustic potash or potassa fusa of the pharmacopoeia. It con- tains impurities, as sulphate and carbonate of potash, chloride and peroxide of potassium, ox- ide of iron, and alumina, from most of which